JS之Base64 与String互转

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
/** Convert data (an array of integers) to a Base64 string. */                                        
                                                                                                  
var toBase64Table = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/';               
                                                                                                  
var base64Pad = '=';                                                                                  
                                                                                                
                                                                                                      
                                                                                                 
function toBase64(data) {                                                                             
                                                                                                 
    var result = '';                                                                                  
                                                                                                 
    var length = data.length;                                                                         
                                                                                               
    var i;                                                                                            
                                                                                                  
    // Convert every three bytes to 4 ascii characters.                                               
                                                                                                   
    for (i = 0; i < (length - 2); i += 3) {                                                           
                                                                                                   
        result += toBase64Table[data.charCodeAt(i) >> 2];                                             
                                                                                                  
        result += toBase64Table[((data.charCodeAt(i) & 0x03) << 4) + (data.charCodeAt(i+1) >> 4)];    
                                                                                                   
        result += toBase64Table[((data.charCodeAt(i+1) & 0x0f) << 2) + (data.charCodeAt(i+2) >> 6)];  
                                                                                                  
        result += toBase64Table[data.charCodeAt(i+2) & 0x3f];                                         
                                                                                                   
    }                                                                                                 
                                                                                                   
                                                                                                      
                                                                                                  
// Convert the remaining 1 or 2 bytes, pad out to 4 characters.                                   
                                                                                                  
if (length%3) {                                                                                   
                                                                                                  
    i = length - (length%3);                                                                      
                                                                                                  
    result += toBase64Table[data.charCodeAt(i) >> 2];                                             
                                                                                                  
    if ((length%3) == 2) {                                                                        
                                                                                                  
        result += toBase64Table[((data.charCodeAt(i) & 0x03) << 4) + (data.charCodeAt(i+1) >> 4)];
                                                                                                  
        result += toBase64Table[(data.charCodeAt(i+1) & 0x0f) << 2];                              
                                                                                                  
        result += base64Pad;                                                                      
                                                                                                  
    } else {                                                                                      
                                                                                                  
        result += toBase64Table[(data.charCodeAt(i) & 0x03) << 4];                                
                                                                                                  
        result += base64Pad + base64Pad;                                                          
                                                                                                  
    }                                                                                             
                                                                                                  
    }                                                                                                 
                                                                                                  
                                                                                              
                                                                                                  
    return result;                                                                                    
                                                                                                   
}                                                                                                     
                                                                                                   
                                                                                                      
                                                                                                   
/** Convert Base64 data to a string */                                                                
                                                                                                  
var toBinaryTable = [                                                                                 
                                                                                                 
    -1,-1,-1,-1, -1,-1,-1,-1, -1,-1,-1,-1, -1,-1,-1,-1,                                               
                                                                                                  
    -1,-1,-1,-1, -1,-1,-1,-1, -1,-1,-1,-1, -1,-1,-1,-1,                                               
                                                                                                   
    -1,-1,-1,-1, -1,-1,-1,-1, -1,-1,-1,62, -1,-1,-1,63,                                               
                                                                                                   
    52,53,54,55, 56,57,58,59, 60,61,-1,-1, -1, 0,-1,-1,                                               
                                                                                                   
    -1, 0, 1, 2,  3, 4, 5, 6,  7, 8, 9,10, 11,12,13,14,                                               
                                                                                                  
    15,16,17,18, 19,20,21,22, 23,24,25,-1, -1,-1,-1,-1,                                               
                                                                                                   
    -1,26,27,28, 29,30,31,32, 33,34,35,36, 37,38,39,40,                                               
                                                                                                  
    41,42,43,44, 45,46,47,48, 49,50,51,-1, -1,-1,-1,-1                                                
                                                                                                   
];                                                                                                    
                                                                                                  
                                                                                                      
                                                                                                  
function base64ToString(data) {                                                                       
                                                                                                   
    var result = '';                                                                                  
                                                                                                  
    var leftbits = 0; // number of bits decoded, but yet to be appended                               
                                                                                                  
    var leftdata = 0; // bits decoded, but yet to be appended                                         
                                                                                                   
                                                                                                      
                                                                                                   
    // Convert one by one.                                                                            
                                                                                                   
    for (var i = 0; i < data.length; i++) {                                                           
                                                                                                   
        var c = toBinaryTable[data.charCodeAt(i) & 0x7f];                                             
                                                                                                  
        var padding = (data.charCodeAt(i) == base64Pad.charCodeAt(0));                                
                                                                                                   
        // Skip illegal characters and whitespace                                                     
                                                                                                   
        if (c == -1) continue;                                                                        
                                                                                                   
                                                                                                      
                                                                                                  
        // Collect data into leftdata, update bitcount                                                
                                                                                                   
        leftdata = (leftdata << 6) | c;                                                               
                                                                                                  
        leftbits += 6;                                                                                
                                                                                                   
                                                                                                      
                                                                                                   
        // If we have 8 or more bits, append 8 bits to the result                                     
                                                                                                   
        if (leftbits >= 8) {                                                                          
                                                                                                  
            leftbits -= 8;                                                                            
                                                                                                   
            // Append if not padding.                                                                 
                                                                                                  
            if (!padding)                                                                             
                                                                                                  
                result += String.fromCharCode((leftdata >> leftbits) & 0xff);                         
                                                                                                   
            leftdata &= (1 << leftbits) - 1;                                                          
                                                                                                  
        }                                                                                             
                                                                                                   
    }                                                                                                 
                                                                                                   
                                                                                                  
                                                                                                  
    // If there are any bits left, the base64 string was corrupted                                    
                                                                                                  
    if (leftbits)                                                                                     
                                                                                                   
        throw Components.Exception('Corrupted base64 string');                                        
                                                                                                  
                                                                                                      
                                                                                                  
    return result;                                                                                    
                                                                                                   
}                                                                                                     
                                                                                                  
                                                                                                
                                                                                                
var str = "";                                                                                         
                                                                                                  
                                                                                                      
                                                                                                   
for ( var i = 0; i < 8192; i++ )                                                                      
                                                                                                
        str += String.fromCharCode( (25 * Math.random()) + 97 );                                      
                                                                                                   
                                                                                                      
                                                                                                  
for ( var i = 8192; i <= 16384; i *= 2 ) {                                                            
                                                                                                  
                                                                                                      
                                                                                                 
    var base64;                                                                                       
                                                                                                   
                                                                                                      
                                                                                                   
    base64 = toBase64(str);                                                                           
                                                                                                 
    base64ToString(base64);                                                                           
                                                                                                  
                                                                                                  
                                                                                                  
    // Double the string                                                                              
                                                                                                  
    str += str;                                                                                       
                                                                                                   
}                                                                                                     
                                                                                                 
                                                                                               
                                                                                               
toBinaryTable = null;